The invention relates to a process and the related contrivance for removing silicon compounds from brine intended for electrolysis. Silicon is normally contained as an accompanying element in the form of silica in rock salt and sodium chloride as found in salt deposits or extractable from sea salt. In brine, silicon is contained in monomer or amorphous form or as polysilica, in agglomerates, and it disturbs the electrolysis process.
According to the conventional state of the art as described, for example, in U.S. Pat. No. 4,274,929 A, the silicon is removed by adding magnesium chloride and increasing the pH value. By means of a very time-consuming mixer-settler process the precipitated silicon can be separated and removed from the brine.
U.S. Pat. No. 4,946,565 A also contains a process for removing silicon compounds from brine. Here, Fe(II) or Fe(III) are used which form a complex with the silicon impurities contained in the brine, the said complex precipitating in a sedimentation tank. Here as well, the process is carried out at an alkaline pH value.
Much the same can be said of DE 2816772 A1. It is claimed that a chemical reagent which can be sodium hydroxide, sodium carbonate, calcium hydroxide, calcium chloride, barium chloride, barium carbonate and/or iron(II) chloride is added to the solution for the precipitation and removal of impurities and a slurry of impurities jointly present with the reagent is simultaneously fed to the solution, thus precipitating the silicon dioxide jointly with the impurities. A pH value of 8 to 11 is adjusted during precipitation of the silicon dioxide together with the impurities.
The above-mentioned processes have the disadvantage that they are very cost-intensive and that the precipitation of the particular silicate must take place at an alkaline pH value and cannot already be carried out in an acidic environment as in the subsequent electrolysis process.